Water chlorination effectively kills bacteria in drinking water, and has been enormously beneficial in controlling the spread of what were once common diseases. The procedure does produce toxins, such as chloromethanes, but it's commonly thought that the identity of these toxins are known and their levels controlled after disinfection.
However, efforts aimed at minimizing these toxins has led to increased levels of previously undetected toxins which may be even more potent. It's a bit unnerving to know that unknown toxins, of greater potency and in unknown levels, are likely lurking in treated water.
Xing-Fang Li (University of Alberta, Canada) and coworkers have added to these concerns. They have discovered a molecule in treated water that is present in low levels, yet is a possible bladder cancer risk.
Fishing for chloroquinones.
The scientists used a combination of electrospray ionization, liquid chromatography, and mass spectrometry to selectively detect chloroquinones in treated water. The basis of their approach is that quinone molecules undergo unique chemical reactions when subjected to electrospray ionization, and the products of the chemical reactions are readily identified.
They consistently found a particular chloroquinone (2,6-dichloro-1,4-benzoquinone, acronym DCBQ) in water, from several treatment plants, that had been disinfected by chlorination or chloramination, followed by UV irradiation. Less DCBQ was found in water further away from the treatment plants, suggesting that the treatment plants were the source of this toxin.
DCBQ isn't stable unless the water is slightly acidic. This suggests that the toxin may not last long after it's produced as a byproduct of water treatment.
Future studies should be aimed at determining how much of this toxin is likely to be ingested by drinking treated water. Even if it's not present in high enough levels to be a concern, it's still a good idea to thoroughly investigate treated water for toxins that are likely byproducts of disinfection, especially those that are of particular public health concern.
Remember that water treatment overall has been enormously beneficial; no one wants a return to cholera and typhoid fever outbreaks. Nevertheless, public health will benefit from increasing knowledge about how to disinfect water in the most safe and effective manner possible.
for more information:
Qin, F., Zhao, Y.-Y., Zhao, Y., Boyd, J. M., Zhou, W., & Li, X.-F. (2009). A Toxic Disinfection By-product, 2,6-Dichloro-1,4-benzoquinone, Identified in Drinking Water Angewandte Chemie International Edition DOI: 10.1002/anie.200904934